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A conundrum...

Discussion in 'General Chat Forum' started by Bilbob, Feb 27, 2012.

  1. Bilbob

    Bilbob Active Member

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    Ok, let's imagine an orbiting space station, where the only means of gravity, are provided centrofugally (sp?) by the rotation of said station...

    When standing on the floor, you are being spun, and therefore physics works to keep you on the floor.

    What if you jumped, to counteract both the gravity effect, and the speed of the spin... would you simply 'hang' or would you return to the 'floor'?
  2. Iccz

    Iccz Active Member

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    Been watching 2001: A Space Odyssey have we? :p


    Space Stations do not have gravity, you can not really create artificial gravity and simulating it isn't a good or practical idea really.

    But yes, you'd land... the only issue is you would not land in the same spot you set off from, you'd actually be jumping forward (or the direction the station is rotating in).

    If you follow...

    I can see this being a messy thread :D
  3. Chadford

    Chadford Active Member

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    Well yes, where's Pincho when you need him for this sort of dilemma?

    :rolleyes:
  4. Bilbob

    Bilbob Active Member

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    ok, you are not actually 'creating' gravity, merely the illusion of, but the ends are the same...

    But again, why would you land? What forces drive you back in the direction of the floor?

    And no, my question was driven by one of those 'mind wandering' moments!
  5. Chox1988

    Chox1988 Well-Known Member

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    Its funny you ask this, was thinking the same myself while playing mass effect (the citadel works that way for anyone thats played it).

    Surely its the same kind of thing as the earth thats spinning, when you jump do you land in exactly the same spot?

    Reminds me of those theme park rides that spin and keep you locked in the spot without harnesses, similar sort of logic just with less force maybe?
  6. imightbewrong

    imightbewrong Active Member

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    If you jump you will carry your momentum - so if the thing is rotating at 10m/s you will be travelling forward at the same speed when you jump - which means you will 'hit the wall' - which just happens to be the bit of floor you left. If it stopped rotating at the moment you jumped, you would 'land' ahead of the jumping position.
  7. Iccz

    Iccz Active Member

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    As your space station is not a vacuum, everything inside it is moving - this includes the air, which is what moves with the rotation of the station :thumbsup:
  8. imightbewrong

    imightbewrong Active Member

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    If you imagine in as an travelator you can see you land where you jump. Now remove gravity, but bend your travelator upwards - ta da!
  9. IronGiant

    IronGiant Moderator

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    If you could jump with enough energy to completely counteract the force holding you to the floor (no idea if you could) you would then be under the action of the air sweeping around in the space station and would end up wherever that moved you. Similarly if you climbed a ladder to the centre and let go you would pretty much stay where you are :)
  10. Chox1988

    Chox1988 Well-Known Member

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    Now thats an interesting concept, the closer you got to the centre the weaker the 'gravity' would get
  11. Iccz

    Iccz Active Member

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    It's actually not as simple as that because you have the coriolis effect to consider as well, so nothing falls in a straight line, but in a curve.



    Edit:
    Assuming it's similar to 2001 - you will not be able to get close enough to the centre to find out :p
    Last edited: Feb 27, 2012
  12. DPinBucks

    DPinBucks Active Member

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    Agreed.

    The gravity effect is provided by the floor pushing on your feet to counteract the centrifugal force, creating a centripetal force. Its magnitude is given by the radius of spin and its speed. If the radius is 10 metres, then to give 1g it must be moving at 10 m/sec.

    As soon as your feet leave the floor, that force no longer applies, but you're still moving at 10 m/s. So you'll go in straight line whereas the floor still has to move in a circle. That means you'll land somewhere 'ahead' (spinwise) of your jumping off point. This is the coriolis effect.

    Note that you'll be in free fall as soon as you jump, so you may get space-sick.

    If you jump fast enough and with a 'backwards' (anti-spinward) component, you'll pass near the axis, but your path will be very curved.
  13. imightbewrong

    imightbewrong Active Member

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    Yep - just like when you jump on Earth :devil:
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  14. DPinBucks

    DPinBucks Active Member

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    True. :( :suicide:
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  15. Bilbob

    Bilbob Active Member

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    Have I missed something? The reason yo udon' spin off into space when you jump on earth is because the mass of the planet genereates an actual gravity field which pulls you back down...
    On the space station, you experience the 'effect' of gravity due to the spinning effect of the station whilst you are in contact with it...
    If you leave contact with it, and as said before, jump also with enough force to counteract the sideways movement, then why would you return to the floor, in the same manner as you would on earth?
  16. Iccz

    Iccz Active Member

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    They were talking about Space adaptation syndrome (Space sickness) and free falling :thumbsup:



    The reason you fall back down is because the air is moving just like the floor would, when the shuttle spins, everything inside it spins with it, and because it's not a vacuum there is air in there, which can also move. So that moves in a similar fashion to the floor, which creates the simulated gravity.

    The sideways movement isn't of much importance as the pseudo-gravity comes from the movement of the floor and/or air.
    Last edited: Feb 27, 2012
  17. DPinBucks

    DPinBucks Active Member

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    I don't think the air has much significance.

    Imagine you're facing the direction of spin, and suppose the floor is moving at 10 metres per second. That is also your speed, and if it weren't for the floor you'd carry on in a straight line.

    But the floor is rotating, and is strong enough to carry you with it. This prevents you from moving in a straight line by accelerating you towards the axis : centrifugal/centripetal force. It is not gravity, but feels like it so long as the radius of rotation is not too small, and you stay in contact with the floor.

    But if you leave the floor by jumping, unlike gravity, which would still apply, you are no longer subject to centrifugal force, and your body would continue forward in a straight line until it reaches that part of the floor directly in front of you (remember that it curves 'upwards').

    The air would try to resist that straight line motion by applying its own centrifugal force, but it wouldn't be very effective because it doesn't have enough mass or friction.

    The point you jumped from will have moved with the floor, of course, but in a circular path, whereas you are now moving staright, both at at 10 m/s. So it has further to travel, and you'd hit the floor a bit ahead of your jumping-off point.
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  18. Iccz

    Iccz Active Member

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    Hmm valid point, the way I got to the air conclusion was imagining being suspended before the motion, then the motion starting, I figured movements in the air would nudge the person, but now you mention it, it would actually be a trivial contribution in comparison.
  19. Bilbob

    Bilbob Active Member

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    Y'see, I was thinking the same as DPin, couldn't imagine the air would have enough mass to cause an effect.
    But I was tired and willing to bow to greater awakeness... :)

    SO are we saying that, if you jumped with enough force to couter the impression of gravity from the rotation, and to counter your sideways movement, then you would, bar slight deviation, keep moving till you hit the other side?
  20. Iccz

    Iccz Active Member

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    It'd be a terrible design if you were able to do that, I imagine it would be more like on 2001 (see picture), with a tube rather than a big open room. Plus even if it was all open, it would most likely be very large, so the chances are you'd no be able to jump high enough anyway. But for the sake of answering your question, should we be able to meet the "Ifs", then yes it would be possible.

    [​IMG]
  21. sheriffwoody

    sheriffwoody Active Member

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    if you were stood on the roof of a car whilst it was doing 70mph, and you jumped as high as you could whilst it was travelling, would the car bugger off from underneth you or would you land back on the roof in the same place?
  22. Iccz

    Iccz Active Member

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    Have you ever put your head/hand out of the window of a moving car?

    If so you feel the air pushing against you, pretty hard, this would be the same if you were standing on the roof of a car, as you have air moving against you, you would not land on the car, never mind in the same place, I imagine you'd probably find it too hard to even properly stand on the car at that speed.
  23. MIghtyG

    MIghtyG Active Member

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    [​IMG]

    If the above represents the space station, the black circle is the spinning surface and the red blob is a person. The green arrow shows which way the thing is spinning.

    When its spinning the forces acting on the red dot are shown by the red arrows. These can be added to show the black line which is the resultant force.

    The Orange line is the pretend force which people would feel as gravity, there isnt actually any force doing this though. This is often refereed to as a centrifugal force which doesnt exist, engineers refer to it as a fictitious force and my old uni professor used to give you a clip on the ear for using it :laugh:

    Anyway, you feel a pretend gravity shown by the orange line. This is due to your own inertia or unwillingness to move. When you accelerate hard in a car or plane the plan is pushing you forward but your body doesnt want to move so it feels like you are being pushed into your seat by something on your chest, this is the exact same here only its the space station pushing up under your feet and your body doesnt want to move so you feel a force holding you down.

    By my understanding if you could apply a force equal to and opposite of the black line you would be able to 'break the gravity' and float. If you generated a force bigger and opposite to the black line you would fly off.

    I could be wrong though.....

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  24. Iccz

    Iccz Active Member

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    Bring us back to the moving air, which would stop you from floating. Plus I think you would still need some movement as the craft would be moving, eventually one of the walls would bump in to you?
  25. MIghtyG

    MIghtyG Active Member

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    Once you are free from the surface of the craft you wouldn't have any forces acting on you and if the craft wasn't moving other than spinning round then you would be free to float.

    Like you say though the air will be moving and this will apply a force to you but it would be minimal, would probably be enough to move you back on the walls of the craft though and once you are back on the wall and moving with it you will have the full effects of the pretend gravity acting on you.
  26. Iccz

    Iccz Active Member

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    Yeah, but what are you floating relative to?
    Let's say we ignore the moving air as a force that will act upon you, you keep floating relative to an external/outside the craft inertial FOR. But the problem is the craft will be moving, so one of the walls will eventually come along and meet you, so while you clould float, you would eventually bang in to something.

    I agree you'll float, but at the same time, it wouldn't be too long as there's always going to be something that means you'll "land" on the floor again.
  27. imightbewrong

    imightbewrong Active Member

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    Consider the difference between jumping on the roof of a car that's doing 70, and jumping in a train carriage that's doing 70.
  28. Flimber

    Flimber Well-Known Member

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    Okay, if you take that space station and stage a 100m race on it with one runner going one way and the other...nah, it doesn't matter...
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  29. MIghtyG

    MIghtyG Active Member

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    [​IMG]

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  30. IronGiant

    IronGiant Moderator

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    You would land pretty much in the same place, probably a bit forwards of where you were when you jumped, but the car wouldn't be there any more :laugh:

    :devil:

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